Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you're attracted to large-cap companies that are consistent earners, have high returns on equity, and are the kinds of companies that growth-at-a-reasonable-price investors would seek out, the new Russell Growth at a Reasonable Price ETF (Nasdaq: GRPC) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The Russell ETF's expense ratio -- its annual fee -- is a low 0.37%.

This ETF doesn't have much of a performance to assess yet, as it's less than a year old. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

What's in it?
The ETF has selected some stocks that have performed well over the past year. Boeing (NYSE: BA) advanced about 11%, with its much-delayed Dreamliner finally debuting. Meanwhile, it also has a big backlog of orders for its 737, and has won some big contracts, such as a $20 billion one from the Air Force.

Other companies haven't done as well lately but could rebound in the future. General Electric (NYSE: GE) gained just 5%, but its management was confident enough in its future to up its dividend by 13% recently. Burned by its commercial lending business, it's shifting away from that, and has been expanding into businesses such as oil and gas equipment.

Construction and mining equipment giant Caterpillar (NYSE: CAT), up 10%, is enjoying strong demand and buying mining equipment maker Bucyrus for nearly $9 billion. The company is also building plants in India and China, positioning itself for growth there.

Networking titan Cisco (Nasdaq: CSCO) sank by about 8% as it retooled itself a bit, killing off less-profitable and less-promising businesses such as its Flip video recorders. Investors are still waiting and watching, though, as its expected revenue growth rate has been falling.

The big picture
A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about the best dividend ETFs. And if you're looking for some great investments beyond ETFs, consider these 10 stocks for your retirement portfolio.